The proponents of this New York Academy of Science symposium met before and after the International Symposium in Lund to select those aspects of brain transplantation which deserved the greatest attention. Two topics, seemingly at either end of a continum, were chosen because of the (1) emergence of new data; (2) need for exchange of techniques and ideas among scientist engaged in basic and applied research; and (3) importance to the progress of neuronal transplantation procedures in clinical medicine. The specific topics selected by us can be grouped into two general areas: molecular and cellular responses in adult brain to donor neural cells and tissues; and models of aging, dementia, and neurodegenerative diseases in primate and subprimate brain. The present proposal begins with three topics central to cellular mechanisms involved in the integration of donor cells with host brain: (1) Interaction of neurons and glial cells, (2) production of trophic substances following transplantation, and (3) transplantation of specific cells. It is expected that the cellular and molecular events underlying the interactions between neurons, glial, and endothelial cells and important insights into procedures to best integrate adult host and donor CNS cells will be thoroughly discussed. The second half of the proposed symposium is devoted to models of aging, dementia, Alzheimer's Disease, Parkinsonism and Huntington's Chorea. The first session will deal with extrapyramidal disorders produced by localized lesions with 6-OH-dopamine and ibotenic acid. The second session deals with aging and dementia. This session presents exciting findings on reversal of age-related deficits by neuronal transplantation and also on the effects of cortical transplants on improving cognitive deficits produced by brain damage. The final session will deal directly with the important topic of brain transplantation into humans and primates. Very recent studies will be presented on MPTP lesioned monkeys and a progress report on the human studies performed in Sweden.